Method for producing wafer notches with rounded corners and a tool therefor

ABSTRACT

A semiconductor wafer for use in the fabrication of semiconductor devices which includes a circular wafer ( 13 ) of semiconductor material having a perimeter and a notch ( 11 ) having a wall disposed in the wafer and extending to the perimeter which includes a preferably rounded apex ( 5 ) interior of the perimeter and a pair of rounded intersections ( 7, 9 ) between the wall and the perimeter. The notch is formed with a tool ( 23 ) for forming rounded corners in the semiconductor wafer which includes a body of a material having a hardness greater than the semiconductor wafer which has a generally rounded or paraboloidally shaped front portion having a forwardmost tip ( 25 ) portion and a wing portion ( 27 ) extending outwardly from the body and having a taper narrowing in the direction of the forwardmost tip portion. The wing portion can be one or more spaced apart wing members or the wing portion can be a single member which extends completely around the tool axis. The notch is formed by rotating the tool and moving the tool in a direction along a radius of the wafer until the wing portion contacts the wafer and forms a rounded intersection between the notch and the wafer perimeter in the shape of the intersection of the rounded tip portion and the wing of the tool.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a method producing wafers with roundedcorners in the notch used for alignment for use in the fabrication ofsemiconductor devices and a tool for producing such wafers.

[0003] 2. Brief Description of the Prior Art

[0004] The fabrication of semiconductor devices generally starts with aslice or wafer of semiconductor material on which the semiconductordevices are fabricated. Such wafers are generally thin in width and havea pair of surfaces with the corners at the perimeter of the wafergenerally being rounded.

[0005] In order to properly align the semiconductor wafers in processingequipment during the fabrication of semiconductor devices on the wafers,it has been necessary to provide a physical indication on the wafer toassist in such wafer alignment. The general such physical indication inthe prior art has been formation of a flat end portion on the otherwisecircular wafer with this indication more recently having been changed toa triangularly-shaped or parabolically-shaped notch at the waferperimeter. A problem with these forms of wafer alignment is that theflat or notch regions used for alignment generally have sharp corners,particularly in the case where notches are used. These sharp cornersgenerate particles during handling which can have deleterious effectsduring subsequent processing operations. In addition, damage from sharpcorners may propagate into the wafer during device fabrication, causingeventual breakage and yield diminution.

[0006] It has also been determined that there is often a thick resistbuildup at the sharp corner made between the notch and the perimeter ofthe wafer which is difficult to remove by ashing and chemical treatment.To date, it has not been appreciated that the sharp edges or cornerslocated in the notch contribute to the above problems and it is notknown that there has been any attempt in the prior art to remove thesharp corners from the notch and the regions connected to the notch.

SUMMARY OF THE INVENTION

[0007] In accordance with the present invention, the above describedproblems of the prior art wafer and particularly such wafer using anotch for alignment are minimized and there is provided a method offabricating semiconductor devices on a wafer having a notch foralignment and tools for effecting such method for minimization of theabove described problem and rounding of the junction of the notch andwafer perimeter as well as the notch apex and edges of the notch runningfrom the wafer perimeter to the notch apex.

[0008] Briefly, there are provided one or more tools in the form of agrinding wheel or belt which rounds all sharp edges or corners existingin the notch either when forming the notch or when altering the shape ofan already existing notch to eliminate all sharp corners both at theapex of the notch as well as along all intersections of the walls of thenotch with the planar wafer surface and also with the perimeter of thewafer. Conventional stress relief etching in hydrogen fluoride plusnitric acid plus phosphoric acid or other suitable acidic solutionsenhances notch corner rounding. In such a solution, rounding occurs as anormal consequence of etching both the top and side surfaces, thecorners etching faster by virtue of being exposed to a greater volume ofetchant. A wafer having a notch with rounded corners reduces thelikelihood of edge damage during wafer handling due to flat finding,wafer centering, etc., prevents thick resist buildup at corners of thenotch during photolithography, eliminates particle contamination fromresist buildup at sharp notch corners and reduces ash time required toremove thick resist buildup.

[0009] The grinding tool provided in accordance with the presentinvention has a rounded front end somewhat in the shape of half of aparaboloid. The tool is formed of a material which is harder than thematerial of which the wafer is made. Generally, the grinding surface ofthe tool is fabricated from diamond with an approximate 800 mesh grit.The tool also includes one or more wing portions extending outwardlyfrom the paraboloid surface and set back from the tool front tip adistance generally equal to the ultimate depth of the notch from thewafer perimeter. The wing is tapered in the direction toward the toolfront tip. In the case of a single wing, such wing can extend completelyaround the entire tool or can extend only partially around the tool. Thetool is rotated it axis which is the major axis of the paraboloid andmoved against the edge of the wafer in a direction along a radius of thewafer either in a predetermined location on the wafer edge or into apreviously formed notch in the wafer perimeter. The tool will grind awaythe wafer to form a notch until the wing or wings contact the perimeterof the wafer. At that point, the tool will grind the corner made betweenthe notch and the wafer perimeter into the shape of the round on thetool between the paraboloid portion of the tool and the wing portion ofthe tool, this being rounded. A second grind step is optionally providedat this time using an identically shaped wheel with finer grit size toremove surface damage, if desired. A third grind step may be provided inorder to round the top edge of the wafer along the intersection of theedge of Th. notch with the top and/or bottom planar surfaces of thewafer. Examples are grinding this surface using a cylindrical grindingwheel rotating against the edge or using a long belt with diamond griton its interior surface that revolves about an axis parallel to the topwafer surface. The tool is then removed with the wafer now ready forprocessing in standard manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a top view of a typical prior art wafer having a notchtherein for alignment;

[0011]FIG. 2 is a view taken along the line 2-2 of FIG. 1;

[0012]FIG. 3 is a perspective view of a tool in accordance with thepresent invention which has just ground a notch in accordance with thepresent invention;

[0013]FIG. 4 is an enlarged view of the rounded corner formed by use ofthe tool of FIG. 3;

[0014]FIG. 5 is a schematic diagram showing a second type of grindingtool which can be used in accordance with the present invention;

[0015]FIG. 6 is a schematic diagram showing a third type of grindingtool which can be used in accordance with the present invention;

[0016]FIG. 7 is a schematic diagram showing the trajectory along thenotch of the grinding wheel of FIG. 6; and

[0017]FIG. 8 is a schematic diagram of a fourth type of grinding toolwhich can be used in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Referring to FIGS. 1 and 2, there is shown in typical prior artwafer 1 having a notch 3 therein. While the perimeter of the wafers inFIGS. 1 and 2 as well as in FIGS. 3 and 4 which are describedhereinbelow are shown to have sharp corners, it should be understoodthat the wafers are generally purchased with the corners along theperimeter away from the notch or flat rounded or these corners arerounded before commencement of fabrication of semiconductor device onthe wafer. As can be seen, there are sharp corners at the apex 5 of thenotch, at the intersections 7, 9 of the notch with the outer edge of thewafer and at the intersections of the notch with the upper and lowersurfaces or opposing major surfaces of the wafer. These corners causethe problems enumerated above and often result in resist buildup,especially on the surface of the wafer on which device fabrication istaking place and where a sharp corner exists, particularly at locations7, 9.

[0019] Referring to FIGS. 3 and 4, there is shown a notch 11 formed in asemiconductor wafer 13 in accordance with the present invention. Theapex 15 of the notch 11 as well as the junctions 17 and 19 of the sidewalls 21 of the notch are rounded. Accordingly, there are no sharp edgeswith the wafer outer edge or perimeter 22 to break off or to causedamage to the wafer during handling.

[0020] The rounded corners are formed by use of a grinding tool 23 asshown in FIG. 3 which is formed of a mesh of diamond grit or other hardmaterial and which has a rounded or paraboloidally shaped nose portion25. Spaced backward from the front tip of the nose portion 25 are one ormore wings 27 having a tapered portion 29 in the direction of the fronttip of the nose portion. The distance between the front tip of the noseportion 25 and the forwardmost portion of the wing or wings 27 is aboutthe depth of the notch 11 which is formed by the tool. The roundedcorners 17, 19 are formed by and take the shape of the tapered portion29 of the wing or wings 27. Though two wings 27 are shown, it should beunderstood that one or more wings can be used and that the width of thewings in a direction around the tool axis can be anything from a smallfraction of the total circumference about the tool axis to the entirecircumference about the tool axis.

[0021] Referring to FIG. 5, there is shown a grinding tool 31 that canbe used in accordance with the present invention for grinding the sharpcorners 33 of a wafer 35. The grinding tool 31 is shown in the form of awheel and is translated toward the wafer surface in the z-direction andthen along an appropriate path in the x- and y-directions to follow thecomplete wafer edge trajectory. The z-position and wheel tilt can beadjusted as the wheel moves farther from the notch edge (increase in yvalue) to produce a gradual edge rounding instead of an abrupt rounding.The wheel position is moved to follow the trajectory of the notch alongits entire extent, Both top and bottom notch corners can be smoothed inthis way. A second step grinding can be provided with a finer grit wheelfor reduction in mechanical damage.

[0022] Referring to FIG. 6, there is shown a further embodiment of agrinding wheel 41 which rotates about the axis of rotation 43. Thisgrinding wheel allows the top edge rounding to be accomplished bymaintaining the wheel without tilt or z-motion by simply translating thewheel around the notch perimeter 45 from the starting position 47 in thedirection of the arrow 49 as shown in FIG. 7.

[0023] Referring to FIG. 8, there is shown a still further embodiment ofa system for rounding the sharp edges 51 of the notch 53. There is showna belt 55 which extends above and below the wafer 57 so that it contactsthe two sharp edges in the notch 53. The interior surface 63 of the belt55 has a diamond grit embedded therein. The belt 55 is moved around thenotch in the direction of the arrows 59 with the belt rotating about itsaxis 61. As the belt 55 is moved around the notch 53, the belt alsorotates about the axis 61 which is also moving with the belt. The beltinterior surface 63 impinges against the corners or sharp edges 51 withthe surface thereof which contains the grit, thereby grinding away androunding the sharp edge. As in the prior embodiment, a subsequent stopcan be a repeat of the grinding process with a belt having a finer grit.

[0024] It can be seen that there has been provided a tool which forms anotch in a semiconductor wafer having rounded corners for purposesalignment during semiconductor fabrication. There is also provided thenotch which has the rounded corners.

[0025] Though the invention has been described with respect to specificpreferred embodiments thereof, many variations and modifications willimmediately become apparent to those skilled in the art. It is thereforethe intention that the appended claims be interpreted as broadly aspossible in view of the prior art to include all such variations andmodifications.

1. A semiconductor wafer for use in the fabrication of semiconductordevices which comprises: (a) a circular wafer of semiconductor materialhaving a perimeter; and (b) a notch having a wall disposed in said waferand extending to said perimeter, said notch including: (i) an apexinterior of said perimeter; and (ii) a pair of rounded intersectionsbetween said wall and said perimeter.
 2. The wafer of claim 1 whereinsaid apex is rounded.
 3. A tool for forming rounded corners in asemiconductor wafer for use in the fabrication of semiconductor devices,which comprises: (a) a body of a material having a hardness greater thansaid semiconductor wafer, said body having: (i) a generally roundedfront portion having a forwardmost tip portion; and (ii) a wing portionextending outwardly from said body and having a taper narrowing in thedirection of said forwardmost tip portion.
 4. The tool of claim 3wherein said body is formed of a material taken from the classconsisting of silicon carbide and diamond.
 5. The tool of claim 3wherein said rounded front portion is in the shape of a paraboloid. 6.The tool of claim 4 wherein said rounded front portion is in the shapeof a paraboloid.
 7. The tool of claim 3 wherein said wing portionincludes a plurality of spaced apart wing members.
 8. The tool of claim4 wherein said wing portion includes a plurality of spaced apart wingmembers.
 9. The tool of claim 5 wherein said wing portion includes aplurality of spaced apart wing members.
 10. The tool of claim 6 whereinsaid wing portion includes a plurality of spaced apart wing members. 11.The tool of claim 3 wherein said body has a major axis and said wingportion extends completely around said axis.
 12. The tool of claim 4wherein said body has a major axis and said wing portion extendscompletely around said axis.
 13. The tool of claim 5 wherein said bodyhas a major axis and said wing portion extends completely around saidaxis.
 14. The tool of claim 6 wherein said body has a major axis andsaid wing portion extends completely around said axis.
 15. A method ofproviding a semiconductor wafer for use in the fabrication ofsemiconductor devices, which comprises the steps of: (a) providing atool having body of a material having a hardness greater than saidsemiconductor wafer, said body having: (i) a generally rounded frontportion having a forwardmost tip portion; and (ii) a wing portionextending outwardly from said body and having a taper narrowing in thedirection of said forwardmost tip portion; (b) providing a circularsemiconductor wafer having a perimeter; and (c) forming a notch in saidperimeter of said semiconductor wafer with said tool.
 16. The method ofclaim 15 wherein said rounded front portion is in the shape of aparaboloid.
 17. The method of claim 15 wherein said wing portionincludes a plurality of spaced apart wing members.
 18. The method ofclaim 16 wherein said wing portion includes a plurality of spaced apartwing members.
 19. The method of claim 15 wherein said body has a majoraxis and said wing portion extends completely around said axis.
 20. Themethod of claim 16 wherein said body has a major axis and said wingportion extends completely around said axis.